Remove backend tests on old inference

Also remove any mentions of NewInference, and rename some tests.

compiler/testData/codegen/box/elvis/genericElvisWithMoreSpecificLHS.kt

@@ -1,4 +1,3 @@
-// !LANGUAGE: +NewInference
 // WITH_RUNTIME
 
 fun test(foo: MutableList<String>?): List<String> {
@@ -14,4 +13,4 @@ fun box(): String {
     if (b.size != 1) return "Fail 2"
 
     return "OK"
-}
+}